Method, apparatus, and tools for precision polishing of lenses and lens molds

ABSTRACT

A tool, apparatus, and method for polishing objects having a wide variety of materials and shapes including precision optical surfaces, injection mold inserts, and thin film coating dies. The tool has an inflatable bladder contained within an abrasive surface. The bladder may be inflated using a variety of fluids having a range of physical properties. The apparatus comprises a multi-axis computer controlled machine to which the tool is attached.

FIELD OF THE INVENTION

A method and apparatus for correcting surface errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for correcting figure errors, and for polishing a wide variety of materials and shapes including but not limited to precision optical surfaces, injection mold inserts, thin film coating dies, and the like. The method of the present invention provides for improving and further finishing of any surface, ranging from a relatively rough ground surface to a polished surface.

Typically the part being finished according to the present invention is measured with a coordinate measurement machine (CMM), a surface profilometer, an interferometer, microscope or some other measuring instrument capable of giving surface roughness and or profile data. The data from such measurement and analysis is then entered into a machine process-controlling computer that then manipulates the data into process parameters for improving or polishing the desired component by a polishing machine of the present invention. One or more iterations of the process of the present invention may be required to achieve the desired results. In the preferred embodiment, a polishing tool comprising an inflatable bladder is attached to and driven by the tool spindle of the polishing machine. The part to be improved or polished, whether spherical, aspherical or parabolic in shape, is placed into the work piece spindle of the polishing machine. If such part is not axially symmetrical, it may be held in a braked position in the work piece spindle, or held in a fixture on a table of the machine. The polishing tool is then compressed against and traversed in a path over the component. Several variables are able to be controlled as process parameters, so that the desired finishing results are achieved.

The present invention provides a method and apparatus for which the main goal is to polish out and remove defects left from a preceding grinding operation or to improve the accuracy of a workpiece such as a lens, mirror, insert for an injection mold, or coating die, such accuracy being relative to the intended use of the workpiece; and also to improve the economy of the polishing process.

In the following specification, for the sake of linguistic simplification, only optical components, also known as precision optics or optics generally, are typically mentioned as the workpiece. However, it is to be understood that all lenses, spherical and aspherical, conformal optics, mirrors, plano shapes, injection mold components, coating dies, and other articles of manufacture that require highly polished accurate surfaces are also included in the description, and are to be considered as being within the scope of the present invention. Materials that may be finished using the method and apparatus of the present invention include, but are not limited to brittle amorphous materials such as e.g., glass, ceramics, infrared materials such as quartz, and the like. Also included are metals such as e.g., tool steel, stainless steel, and the like; crystalline materials such as e.g. silicon; and any other workpieces requiring high finish and form specifications.

Currently, many optical lenses are made beginning with a “blank” starting part (such blank part being an approximately formed and generally roughly finished piece) in several processing steps. The process steps typically include fine grinding, followed by conventional polishing techniques wherein the surface roughness and surface accuracy of the lens is significantly improved. This prior art process is sufficient for many conventional low-precision lenses, but when the desired lens has a shape that is not spherical or plano and/or where such conventional methodologies cannot be applied e.g., aspherics, or where the lens has very high accuracy requirements, such prior art process is not sufficient. In such circumstances, the method and apparatus of the present invention is advantageous.

In particular, several prior art procedures are known to the applicants as being used to fabricate precision optics. One of these procedures is known in the art as small spot tool polishing, wherein a pencil like polishing tool (typical 5 to 15 millimeters in diameter) is used, such tool comprising a polishing medium of polyurethane, felt, pitch or some other combination of polishing material bonded thereto, and typically known as a foil.

In one specific embodiment of the small spot tool polishing process, a polishing tool, rotating around the axis thereof, is mounted to a robotic arm and is traversed by such arm across the lens surface, or alternatively, such tool is built into a computer numerically controlled (CNC) polishing machine. During the process a polishing suspension is applied, while the polishing tool is traversed across the lens surface through a predetermined typically computer controlled path. Depending on the correction geometry required, different volumes of material are abraded, or polished, from the lens surface. The robotic arm of the correction machine is programmed in such a way that the polishing tool is moved with different dwell times at different positions as such tool passes over the lens. Thus, when more material must be removed at a particular location, the dwell time is increased, and vice versa. During the polishing process, the lens may be rotate around its axis, or be it may be fixed in specific positions if the robotic arm of the correction machine has such capability.

In the small spot procedure there are several disadvantages. The polishing tool wears quickly due to its small diameter, which results in the distinct disadvantages of a) typically very long polishing cycles; and b) because of quicker degradation of the small polishing foil it is much more difficult and costly to develop accurate corrective polishing routines. Another disadvantage is due to the small spot diameter of the tool. Material removal rates are typically very slow, since the performance is directly proportional to the size of the surfaces that are in contact during the polishing routine.

Another known finishing/polishing procedure is known as magnetorheological finishing (MRF). With the use of the MRF process, marked improvements in surface roughness and accuracy can be achieved. In general, the MRF process produces better results than small spot polishing. Reference may be had e.g., to U.S. Pat. Nos. 5,795,212, 6,106,380 (deterministic magnetorheological finishing), U.S. Pat. No. 5,839,944 (apparatus deterministic magneto-rheological finishing), U.S. Pat. No. 5,971,835 (system for abrasive jet shaping and polishing of a surface using a magnetorheological fluid), U.S. Pat. No. 5,951,369, 6,506,102 (system for magnetorheological finishing of substrates), and U.S. Pat. Nos. 6,267,651 and 6,309,285 (magnetic wiper). The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

With the MRF procedure a polishing suspension is used, which contains particles that can be magnetized and therefore under the effect of strong electromagnets can be solidified. A polishing suspension is applied sequentially on the outside surface of a cylinder rotating around its horizontal axis. The polishing suspension is disposed in a thin band upon the outside surface of a rotating cylinder, and is conveyed to a location where a strong magnetic field is focused. This field is created by magnets surrounding both sides of the wheel. Under the influence of the magnetic field, the polishing suspension increases in viscosity until it is substantially an abrasive solid, thereby forming a stiff polishing body, which becomes the polishing tool. Thus within this area i.e., in the upper apex of the polishing tool, a lens may be polished by such solidified MRF fluid. As the wheel rotates the polishing suspension leaves the contact area of the lens and the magnetic field, and is then vacuumed/wiped off of the wheel and continuously recirculated.

During the MRF polishing process, the lens rotates. The lens carrier with the lens can be placed by means of a tilting device and an assigned axis control at angles to the vertical axis. With a large angle of inclination, the edge of the lens touches the polishing tool, while with a small angle of inclination the center of the lens comes into contact with the polishing tool. Additionally the lens carrier is guided in such a way that it also can execute vertical movements. With a rotating lens, the angles of inclination are continually varied; such variation is accomplished with the use of virtual pivot point computer controlled motion that combines the two linear and one rotary axes and thus keeps the lens in consistent contact with the polishing tool. A spiral develops on the lens that is the trajectory of the point of contact between the solidified polishing suspension and the lens surface.

The different material removals necessary for the correction of the lens geometry are implemented as follows: The dwell time of the point of contact on a certain area on the lens surface can be varied by appropriately controlling the courses of motion. Since the material removal is proportional to the dwell time, the desired corrections can be achieved. The polishing suspension in its “firmness” can be influenced by variation of the magnetic field strength. This further enables different material removal rates. A further correction option results by varying the depth of submergence of the lens into the polishing suspension.

Although the MRF process has many attributes, such process also has some distinct disadvantages as follows: 1) Cost-effective polishing of deviations is limited to errors of less than 200 nanometers only. This is a result of the lack of “stiffness” of the magnetically stiffened polishing suspension and the ability to shear/polish features greater in magnitude. 2) There is a very high capital cost of entry into the MRF technology. The process entails very complex technology, which also increases the cost of operation. It is also necessary to continuously change the MRF polishing suspension, which is very expensive because of its proprietary nature. 3) Parts made of magnetic materials are not able to be polished with this process, as the workpiece will become magnetized and not release the magnetic process fluid. 4) Small concave parts cannot be polished due to the configuration and size of the MRF polishing wheel.

Reference may be had to German patent DE0031057 of R. Mandler, the disclosure of which is incorporated herein by reference. There is disclosed in such patent a method for polishing of lenses and mirrors for high resolution optics. The lens/mirror is polished conventionally and measured by interferometric means to map the surface and to determine how much material needs to be removed and from where. The lens is supported on a rotating holder with two degrees of movement, while the polishing wheel is supported with axial adjustment. The polishing wheel has a flexible rim-inflated with a variable internal pressure to adjust the hardness of flexible rim/tire. Mandler relies upon changes in pressure on a polyurethane foil to impact removal rates and finishing qualities. Although as stated therein, the apparatus of Mandler can change the pressure during the process, such process does not have the ability to change to softer media, such as felt or other softer synthetic materials as is disclosed and claimed in this application. Mandler also discloses only a 3-axis process, whereas embodiments of the present invention include control and operation with respect to five or more axes.

With the method and apparatus of the present invention, many of the disadvantages of the aforementioned techniques are non-existent, or rendered insignificant. It is therefore an object of this invention to provide an apparatus for precision polishing of objects comprising a wide variety of materials and shapes.

It is a further object of this invention to provide a versatile and adjustable tool for precision polishing of objects comprising a wide variety of materials and shapes.

It is another object of this invention to provide a method for precision polishing of objects comprising a wide variety of materials and shapes.

It is an object of this invention to provide a method and apparatus for precision polishing of objects that is simple and has a low operating cost.

It is an object of this invention to provide a method, a tool, and an apparatus that in having the ability to remove low, mid, and high spatial surface errors, reduces the requirements of the pre-fine grind tolerances, which in turn reduces the requirements of the fine grinding apparatus.

It is an object of this invention to provide a method and apparatus for precision polishing of objects that has a high rate of material removal.

It is an object of this invention to provide a tool for precision polishing of objects that has high longevity and stability of operation.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a polishing tool comprising a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder; and a passageway disposed within said mandrel between said cavity and the exterior of said mandrel.

In accordance with the present invention, there is provided an apparatus for polishing objects comprising a first linear slide movable along a first axis, disposed upon a base; a first rotatable spindle engaged with said first linear slide, said first rotatable spindle further comprising a first chuck, and said first rotatable spindle aligned with said first axis; a second linear slide movable along a second axis, engaged with said first linear slide, with said second axis disposed orthogonally to said first axis; a second rotatable spindle engaged with said second linear slide, said second rotatable spindle further comprising a second chuck; and a polishing tool engaged with said second chuck of said second rotatable spindle, said polishing tool comprising a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder; and a passageway disposed within said mandrel between said cavity and the exterior of said mandrel.

In accordance with the present invention, there is provided a method of polishing a surface of an object using a machine tool apparatus comprising a polishing tool comprised of a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder; and a passageway disposed within said mandrel between said cavity and the exterior of said mandrel, comprising the steps of preparing said polishing tool for said polishing of objects; preparing and programming said machine tool for said polishing of objects; executing a first polishing cycle with said machine tool apparatus, wherein said polishing tool is in contact with said surface of said object; and measuring said surface of said object.

The method and apparatus of the present invention is advantageous because it is simple and lower in cost compared to other approaches, and it can be adapted for the polishing of a variety of materials and shapes. As a result of the invention, articles of manufacture such as precision optics, injection mold inserts, and thin film coating dies can be polished with high precision at a high throughput and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which:

FIG. 1 is a schematic representation of one preferred polishing apparatus of the present invention;

FIG. 2A is a cross-sectional view of one preferred polishing tool of the present invention;

FIG. 2B is a side elevation view of the polishing tool of FIG. 2A, in the process of polishing a convex lens;

FIG. 3 is a cross-sectional view of another preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A;

FIG. 4 is a cross-sectional view of one preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A;

FIG. 5 is a flowchart depicting a method of assembly of the preferred polishing tool of FIG. 2A;

FIG. 6 is a flowchart depicting a method of preparing the preferred apparatus of FIG. 1 for a polishing operation; and

FIG. 7 is a flowchart of a complete method of polishing an optic using the apparatus and polishing tool of the present invention.

FIG. 8A is a cross-sectional view of another preferred polishing tool of the present invention;

FIG. 8B is a side elevation view of the polishing tool of FIG. 8A, in the process of polishing a concave lens; and

FIG. 9 is a schematic representation of another preferred polishing apparatus for polishing concave spheres, aspheres, convex spheres, or other conformal shapes.

The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In describing the present invention, the following term(s) have been used in the description:

As used herein, the term figure error (or form error) is the measured global deviation from the desired surface shape e.g, a sphere, asphere or polynomial geometric shape.

As used herein, form error is a low frequency error. Traditionally in optics, irregularity and power are the two specifications that need to be considered. Irregularity is the deviation from a perfect surface. Power is the resulting average surface dimensions e.g., radius of curvature.

As used herein, the term zonal enhancement is meant to indicate a correction of the figure error, which is located symmetrically or asymmetrically at one specific location (zone) on the work piece. For example, if a cylindrical disc was the workpiece, a zonal error would be in one sector of the disc, or in a specific band or ring on the disc, or other rotationally symmetrical part.

As used herein, the terms spot, high, mid- and low spatial frequencies in reference to errors in a surface to be polished are meant to indicate the following. Low spatial frequencies are errors that appear only once to a few times across a particular surface. Mid-spatial frequencies are errors that occur many times across a surface of a part, generally have a periodic spacing of between 80 microns and 3 mm, and are typically caused by cutter marks due to machine or tool vibrations. High spatial frequencies are errors that happen on a microscopic scale, which may appear thousands of times across the surface of a part, and have a periodic spacing of less than 80 microns.

As used herein, the term polishing, when used in reference to a workpiece to be finished, is meant to indicate a chemo/mechanical process that ablates material from a surface.

As used herein, the term correction of form, or form error modification correction, when used in reference to a workpiece to be finished, is meant to indicate the same as has been defined for figure error.

As used herein, the term figure, when used in reference to a workpiece to be finished, is meant to indicate polishing in a correction for error in the figure and or form, which are the same.

As used herein, the term surface roughness, when used in reference to a workpiece to be finished, is meant to indicate high frequency errors, which are typically the result of brittle fracture regime (e.g. microcracks).

FIG. 1 is a schematic representation of one preferred polishing apparatus of the present invention. Referring to FIG. 1, polishing apparatus 100 is configured for polishing convex spheres, aspheres, shallow concave spheres, or other conformal shapes. Polishing apparatus 100 comprises a base 102 that supports Y-axis linear slide 104, the motion of which is bi-directional along Y-axis 105 (directed perpendicular to the plane of FIG. 1). Linear slide 106, the motion of which is bi-directional along X-axis 107, is mounted upon Y-axis linear slide 104. These linear slides 104 and 106 are both computer numerically controlled (CNC) positioning devices, providing programmable motion in the X-Y plane.

Workpiece spindle 108 is mounted upon linear slide 106, such that the motion of spindle 108 is bidirectionally programmable along axis 109, which is parallel to X-axis 107. Thus spindle 108 is movable by computer control along axis 109, depending on the requirements or the polishing process. Rotatable workpiece chucking device 110 is attached to end of workpiece spindle 108. The workpiece 10 to be polished is engaged and held by chuck 110 and rotated by spindle 108 around the central rotary axis thereof.

Apparatus 100 further comprises vertical slide 120 attached to polishing machine column 122, which is joined to base 102. The motion of vertical slide 120 is bi-directional along Z-axis 121. Polishing tool spindle 124 is attached to the Z-axis slide 120. The rotational speed (RPM) of this spindle is varied by the computer depending on the desired removal rate of material from workpiece 10. Apparatus 100 further comprises a rotatable chucking device 126 attached to the end of polishing tool spindle 124, in which polishing tool 128 of the present invention is inserted and rotated. Polishing tool 128 is provided in a variety of shapes, sizes, and materials (e.g. see polishing tool 200 of FIGS. 2A and 2B), as will be described subsequently in this specification.

In summary, there are three linear and one rotary axis drives in this configuration, all of which are computer controlled to allow for a deterministic polishing process, to be described subsequently in more detail in this specification.

Referring again to FIG. 1, in the preferred embodiment, apparatus 100 further comprises a fluid delivery system 130 for delivery of a homogeneous liquid or a liquid slurry. In some embodiments, delivery system 130 delivers a liquid containing finely divided solid particles, and as such is considered a slurry, a suspension, or a particulate dispersion. Such particles are preferably abrasive polishing particles with a hardness sufficient to wear a typical optical material such as e.g. glass. Such particles may comprise e.g., silica, alumina, ceria, diamond, and the like, and mixtures thereof. Many other hard, abrasive particulate materials such as e.g., carbides, nitrides, etc. will be apparent to those skilled in the art.

In other embodiments, delivery system 130 delivers a homogeneous liquid substantially free of solid particles. Suitable liquids may be e.g. water, water soluble oils or lubricants (such as e.g. glycerine), hydrocarbon oils, silicone oils, and the like. The selection of a particular homogeneous liquid or a particulate slurry will depend upon the particular optical part being polished, and upon the desired end results.

Referring again to FIG. 1, slurry or fluid delivery system 130 comprises a reservoir (not shown), a slurry/fluid mixer 132, and a slurry/fluid pump 134. Slurry/fluid delivery system 130 is used to supply an abrasive slurry/fluid (not shown), which is delivered through conduit 136 and directed by nozzle 138 upon the polishing tool 128 and workpiece 10, at the area of contact there between.

FIG. 2A is a cross-sectional view of one preferred polishing tool of the present invention used in apparatus 100 of FIG. 1, according to the methods of the present invention. Referring to FIG. 2A, polishing tool 200 comprises a main body or bladder mandrel 202 having a shank 201 at a proximal end 224 thereof, and a flange 211 at a distal end thereof, around which a bladder 204 is disposed and sealably engaged therewith. Compression washers 206 and 207 are disposed on both sides of bladder 204, and are held in place by locking nuts 208 and 209, respectively. Nuts 208 and 209 and washers 206 and 207 provide sealing means in that nuts 208 and 209 and washers 206 and 207 hold bladder 204 tightly against flange 211 of mandrel 202. In the preferred embodiment, lips 246 and 248 of bladder 204 are disposed and held firmly in grooves 242 and 244 of mandrel 202, so that bladder 204 is sealed to mandrel 202.

End 210 of mandrel 202 has an axial bore 212 disposed therein, which is connected to at least one radial bore 214, or preferably a plurality of radial bores 214 extending to a cavity 216 disposed in the perimeter 218 of mandrel 202. Such axial bore 212 and radial bores 214 form a continuous passageway such that cavity 216 is in communication with the atmosphere outside of tool 200. Thus axial bore 212 and radial bores 214 allow the cavity 216 to be filled and pressurized with a fluid delivered through inflation device 220, which is disposed and sealed in axial bore 212 at the end 210 of mandrel 202.

Polishing tool 200 further comprises a ring assembly 230 of polishing material disposed around the outer perimeter of bladder 204. FIG. 3 is a cross-sectional view of one preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A. Referring to FIG. 3, ring assembly 230 is a dual ring assembly comprising a backer ring 232 of material, over which is disposed abrasive ring 234 comprised of a polishing medium adhered thereto. The resulting polishing ring assembly 230 is disposed around the perimeter of and contiguous with bladder 204. In one preferred embodiment, backer ring 232 consists essentially of a band of poly(ethylene terephthalate) having a thickness of between about 50 microns and about 1000 microns, and a width of between about 2 millimeters and about 30 millimeters.

Abrasive ring 234 is made of a material of sufficient structural strength to withstand the high shear and tensile forces during polishing, and to resist degradation through exposure to the polishing/lubricating fluid, such as e.g. polyurethanes of various durometers; and various types of felt, cork, and metal and/or resin bond diamond, alumina, and/or zirconium, with a multitude of different types of backings and patterns therein. Abrasive ring 234 preferably has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 2 millimeters and about 30 millimeters.

FIG. 4 is a cross-sectional view of another preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A. Referring to FIG. 4, ring 230 simply comprises a single ring 236 of polishing material disposed around the perimeter of bladder 204. The embodiment of FIG. 4 is used when ring 236 is of sufficient structural strength so as to be able to perform the particular polishing process without the use of a supporting ring disposed contiguously with such ring, as was depicted in FIG. 3. In one preferred embodiment, single ring 236 consists essentially of polyurethane, and has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 2 millimeters and about 30 millimeters.

FIG. 2B is a side elevation view of the polishing tool of FIG. 2A, in the process of polishing a convex lens. Referring to FIGS. 2A and 2B, polishing ring assembly 230 (also known as the foil) is disposed around the outer perimeter of bladder 204 and held in place while bladder 204 is pressurized with a fluid. In operation, polishing tool 200 comprising polishing ring assembly 230 is rotated and engaged with lens 10 such that polishing ring assembly 230 provides a shearing and polishing action upon the surface of lens 10. It will be apparent that the pressure that is applied to bladder 204 will determine the curvature and firmness of the outer surface of polishing ring assembly 230 during a polishing operation.

Referring again to FIG. 2A, and in one preferred embodiment, bladder 204 has a shape and cross sectional profile that is substantially similar to that of a tire. Bladder 204 is preferably made of a compliant, flexible elastic material that is wrapped or attached at its periphery to the perimeter 218 of mandrel 202. Suitable materials for bladder 204 are e.g., natural or synthetic rubber, silicone, or polyurethane, with a wall thickness of approximately 1 millimeter.

The tire-shaped bladder 204 may have a variety of specific cross sectional shapes. Before inflating bladder 204 with either air or some other fluid, polishing foil 203 is disposed around or applied to the bladder tool to act as the polishing medium. In one further embodiment, polishing foil 230 is made of polyurethane, and the abrasive polishing medium is provided in a liquid slurry that is pumped onto workpiece 10 and polishing foil 230, as described previously. Alternatively, abrasive particles may be embedded in the polishing foil. Suitable abrasive particles include particles made by the Rhodes Corporation, or by the Minnesota Mining and Manufacturing Company (3M), or it may actually be a product that has In a further embodiment, abrasive particles in the shape of miniature pyramids of polishing medium such as e.g., alumina in varying grit sizes is used. Such products will require that only water be added to wet the polishing medium (the dry powder.)

In another embodiment, foil 230 comprises a backer ring of poly(ethylene terephthalate) (PET) or similar material to allow softer polishing ring media to be used without tearing or pulling apart, yet maintaining the flexibility required for fine polishing. Bladder 204 of tool 200 is then inflated to a specific pressure depending on the polishing results desired. In such an embodiment, foil 230 is held in position upon bladder 204 by the expansion pressure of the bladder 204 being inflated; thus no adhesive or mechanism is required to bond foil 230 to bladder 204. Such a configuration enables a simple and rapid change of foil polishing media.

In operation of apparatus 100 of FIG. 1, to which is fitted polishing tool 200 of FIG. 2A, several factors will affect the accuracy and removal rates of the polishing process: the size and shape of bladder 204, the composition of the polishing medium, the composition of the polishing slurry, and the pressure applied to the bladder 204 and also the type of fluid used to inflate the bladder. These latter variables are related to the tool itself (with the exception of slurry composition). Also affecting the accuracy and removal rates of the polishing process included in this invention are variables of the apparatus, such as e.g., example spindle speeds, axis feed rates and polisher path modifications.

It will be apparent that a variety of fluids may be used to pressurize bladder 204 of polishing tool 200, and that the physical properties of such fluids, as well as the pressure of such fluids also will affect the accuracy and removal rates of the polishing process. The fluid may be selected so as to beneficially affect the polishing process. In one simple and thus preferred embodiment, air is used as the bladder inflation fluid. In another embodiment, a much more dense fluid, i.e. a liquid, such as water is used as the bladder inflation fluid. In such an embodiment, the effective pressure of the outer wall of the bladder is a function of not only the inflation pressure, but also the rotational speed. Such rotational speed provides an additional pressure component due to the centrifugal force exerted by the fluid, in proportion to the square of the rotational speed. Such pressure is analogous to the pressure at the base of a column of liquid acted upon by gravity.

In a further embodiment, a viscous liquid, such as a hydraulic oil is used as a bladder inflation fluid. The viscosity of such a viscous liquid is preferably between about 10 centipoise and about 100,000 centipoise, and more preferably between about 20 centipoise and about 1000 centipoise. The higher viscosity of such fluid also affects the accuracy and removal rates of the polishing process, because at the contact area of the bladder with the workpiece, the bladder is deformed; hence the fluid disposed within the bladder must undergo viscous flow in this region. Thus a higher viscosity fluid has a greater resistance to deformation, and also being non compressible and thus can provide a beneficial polishing effect. In yet another embodiment, the use of a viscous fluid provides vibration damping to the process, thereby rendering such process more precise, stable, and reliable. In further embodiments, non-Newtonian fluids are used such as e.g. a shear thinning fluid, or a shear thickening fluid. In other embodiments, fluids for which the rheology may be varied by exposure to an electric or magnetic field may be used.

Referring again to FIG. 2A, in one embodiment, inflation device 220 is a simple, inexpensive check valve. In a preferred embodiment, inflation device is a valve stem, commonly used for the inflation of tubeless tires. In another embodiment, axial bore 212 is sealed, and mandrel 202 of tool 200 is provided with a second axial bore 222 disposed through the opposite end 224 of mandrel 202. In such an embodiment, axial bore 212 is supplied with pressurized fluid from a fluid supply means (not shown) in real time during the polishing process. Such fluid supply means is commonly used as a coolant supply to a machine tool and is well known in the art of machine tools. Thus the pressure within bladder 204 may be varied and/or pulsated during the polishing process, by the delivery or withdrawal of bladder inflation fluid as indicated by arrow 225.

It is to be understood that many multi-axis CNC machine tools are known in the art, which can be suitably configured to use the polishing tool and the methods of the present invention. The particular configuration of machine tool will depend upon the material properties, size, and shape of the starting blank and the desired finished end product. The present invention is not limited only to the use of the machine tools described herein. For example, such a machine tool could comprise from between two computer controlled axes up to as many as five or six computer controlled linear and/or rotary axes.

Referring again to FIG. 1, polishing tool 200 and workpiece 10 to be polished are typically inserted into separate spindles 124 and 108 of a multi-axis CNC machine tool. Machine tool apparatus 100 could have a configuration as shown in FIG. 1, or a configuration similar to that of a lathe, mill or some other customized arrangement of the axes, depending upon the part to be polished. Work piece spindle 108 may also be programmed to maintain constant surface speed and also to do zonal enhancements that are especially necessary when there are axial asymmetries in the part. It is to be understood that many different machine variations are possible, and that axes and spindles can be configured in a multitude of combinations/permutations to suit any workpiece shape that needs to be polished. The configuration of the different machine axes and spindles can be in any order as required to enable articulation of the polishing tool over the surface of the workpiece to be polished. Accordingly, all such configurations are to be considered within the scope of the present invention.

During the polishing operation, the polishing slurry/fluid suspension is fed between the polishing tool 200 and the work piece 10 by slurry delivery system 130. Depending on the results required, the axis traverse feedrates (i.e. the velocities of the linear slides), the workpiece rotational speed in revolutions per minute (RPM) and tool spindle rotational speed in RPM, and the tool path variation in three dimensional space are adjusted via automated computer control.

In one embodiment, the pressure (and thus the “firmness”) of bladder 204 of polishing tool 200 is preset, and maintained constant during the polishing operation. Depending on the bladder shape, the bladder material properties, the bladder inflation pressure, and the hardness/density of polishing foil 230, a specific pretest is performed in order to characterize the polishing spot profile. As used herein, the term spot profile is meant to indicate the indentation resulting from contacting a test workpiece with polishing tool 200 or 300 by moving the otherwise stationary test workpiece into contact with the polishing tool 200 or 300, thus leaving a depression, indentation, or “footprint” in the part, the test is performed in a standard manner, with the workpiece moved against the tool with a specified displacement for a specified period of time. The resulting volume of the indentation per unit time period it the material removal rate.

Thus the shape and size of the area produced when the polishing tool is pressed into the test piece for a given period of time is the spot profile. This spot profile is then used in the generation of the time dependent trajectory of the polishing tool over the surface of the workpiece that is required to achieve the desired polishing results. This time dependent trajectory is also known in the art as the tool path and dwell times used in polishing. With the profile characterized, high, mid and low spatial features can be greatly improved through adjustments of the polishing variables, tool rpm, workpiece rpm, axes feedrates, and compression factor. As used herein, the term compression factor is meant to indicate the compressive force applied by the polishing tool against the workpiece, such force being the combination of force due to bladder pressure, and force due to the trajectory of the tool against the workpiece.

Referring again to FIG. 1, the work piece spindle 108 holds workpiece 10, i.e. the optic or other part to be finished. Work piece spindle 108, and/or polishing spindle 124 as described are attached to computer controlled linear or rotary slides 104, 106, 108, and 120 so that any path or desired motion and dwell times of the polishing tool 200 over the workpiece 10 can be achieved. As described previously, workpiece spindle 108 also acts as a servo controlled positioning axis, the motion of which may be controlled in coordination with the described linear and rotary motions such that any non-axially symmetric irregularities, zonal enhancements, in the workpiece 10 may be also corrected with the polishing method of the present invention. Polishing tool spindle 124 is controlled via a motor and spindle drive (not shown) such that the rotation speed in RPM is variable, and may be adjusted during the polishing process, depending on the process and workpiece requirements.

As was described previously, there are machine configurations for apparatus 100 that can be provided, depending on the workpiece shape and size, and the desired finished workpiece results. The motions of these axes may be combined so as to not only provide straight, linear, or arcuate motions of the polishing tool 200, but also to provide zigzag, sinusoidal, rotary or other programmable oscillations, in order to achieve the amount of material that is to be removed and to achieve the resulting surface quality.

Based on the configuration of the machine 100, the spindles and linear and/or rotational slides thereof, and the type/form or the polishing tool(s) to be used, there are various steps required in the process of the present invention, which results not only in the polishing of the workpiece, but also the correction of the surface errors/form of the workpiece.

In general, the pre-machined (i.e. unfinished) workpiece may be measured with a surface profilometer, an interferometer, a CMM or any other type of measuring device capable of analyzing the geometric shape, in order to quantitatively define the basic starting condition of the workpiece. This information is required to begin the process of improving the components surface roughness, mid-spacial frequency (waviness) and figure. After the analysis, the acquired data on the workpiece is then communicated into the computer control on the machine. This information, along with the software built into the computer control, calculates the process parameters/motion control required giving the desired workpiece improvements.

The polishing tool spot size and shape is either known based on a library of predetermined empirical parameters obtained experimentally, or it is analyzed through a series of tests. The polishing tool spot size and shape is then sent to the CNC controller. This data is the additional information needed to develop the required polishing tool path motion and speed, and spindle rotational and linear speeds to achieve the desired process results. It is to be understood that the polishing spot size may be affected by the size, shape, material properties, and fill pressure of the bladder, fluid type of the filled bladder, and the polishing foil material properties.

A more detailed description of methods for using the polishing tools and the apparatus of the present invention will now be described. It is to be understood that the steps in the following descriptions are illustrative of some embodiments of methods, but that the order of the steps described herein may be changed, while still achieving substantially the same end results. Thus, such variations in the methods described herein are to be considered within the scope of the present invention.

A first preferred step, based upon experience and knowledge of the finishing process and the previously described data obtained on the unfinished part, is to assemble and fit a polishing tool to the polishing apparatus. FIG. 5 is a flowchart depicting a method of assembly of the preferred polishing tool of FIG. 2A in the apparatus of FIG. 1. Referring to FIG. 5, FIG. 1, and FIG. 2A, tool setup process 410 begins with step 412, wherein polishing tool 200 sans polishing ring assembly 230 is fitted in holding chuck 126 of spindle 124. Subsequently in step 414, polishing ring assembly or foil 230 is selected and fitted to bladder 204 of polishing tool 200. Bladder 204 is inflated to hold polishing ring assembly 230 in place thereupon in step 416. A measurement of the center height of polishing ring 230 is made with suitable measuring means such as e.g., a dial indicator, a caliper, a micrometer, and the like in step 418. With steps 412-418 completed, tool setup process 410 is complete. Alternatively or additionally, an alignment fixture may be used to aid in proper position/alignment of the foil and or reinforcement ring

The overall preparation/setup of the polishing apparatus then follows. FIG. 6 is a flowchart depicting a method of preparing the preferred apparatus of FIG. 1 for a polishing operation. Referring to FIG. 6, and FIG. 1, apparatus or machine setup process 420 begins with step 422, installing the completed polishing tool assembly 200 in chuck 126 of spindle 124. (Step 422 is performed in the event that tool 200 was removed from spindle 124 in order to make the measurement 418 of tool setup process 410 of FIG. 5, or if tool 200 was setup separately from machine 100.)

Machine setup process 420 continues with step 424, in which the polishing tool dimensional data obtained in measurement step 418 is entered into the CNC process controller of machine 100. The unfinished optic or other workpiece to be polished is then placed into holding chuck 110 of spindle 108 in step 426. The data obtained from measurements made on the unfinished optic that have been described previously are also entered into machine 100 in step 428. In step 430, an analysis of the spot size/removal function of the polisher on the optic is performed, or such data from a previously described library of tool functions is entered into the CNC process controller. In step 432, the CNC process controller is further programmed with polishing tool and polishing medium parametric data such as removal function, polishing spot size, polishing tool medium/material type, polishing tool dimensions/shape, polishing tool bladder pressure, optic/workpiece starting and finished dimensions, and polishing slurry type/composition.

With all of the relevant data programmed into the CNC process controller, the deterministic path of the polishing tool 200 on the optic 10 is calculated by such controller in step 434. In performing machine setup process 420, depending on the shape and size of the workpiece 10, coordinate offsets will be established in all of the programmable axes 104, 106, 108, and 120, so as to provide the CNC controller of machine 100 the information/location of part 100 such machine 100 will begin the polishing process at the correct location on workpiece 10. At this point, with machine setup 420 complete, some test probing of the workpiece 10 and/or the polishing tool 200 may be implemented to confirm that such starting location is correct. Once the CNC controller of machine 100 has defined/confirmed the “part zero” or starting position of polishing tool 200 upon workpiece 10, the polishing process may begin.

FIG. 7 is a flowchart of a complete method of polishing an optic using the apparatus and polishing tool of the present invention. Referring to FIG. 7, tool setup process 410, and machine setup process 420 are performed according to the foregoing descriptions of FIG. 5 and FIG. 6. Subsequently, in step 440, the optic polishing cycle is performed, wherein a computer developed path of polishing tool 200 upon workpiece 10 is performed. As described previously, the workpiece spindle 108 and polisher spindle 124 are placed in rotary and linear motion along one or more of axes 105, 107, 109, and 121, depending on the desired results. Note that in some embodiments the part may not be attached to a rotating spindle and may be held in a stationary position, while polishing tool is articulated over the surface thereof.

In some circumstances, more than one bladder-polishing tool may be required to achieve the desired results in polishing workpiece 10. Accordingly, in one embodiment (not shown), machine 100 is provided with automatic tool changers, to change between multiple polishing tools during the process. In another embodiment (not shown) multiple spindles are provided on machine 100, wherein a first polishing tool on a first spindle performs part of the polishing operation, a second polishing tool on a second spindle performs part of the polishing operation, and so forth, to the extent that multiple tools and spindles are provided on machine 100.

In the preferred embodiment of polishing cycle 440, but not in all embodiments, at such time when the spindles 108 and 124 have started, but before any motion of tool 200 along axes 105, 107, 109, and 121, there is provided and injection or pumping of a specific polishing slurry or other fluid at the contact location of polishing tool 200 with workpiece 10, which enhances the polishing action or removal rates of material from workpiece 10. As described previously, the path of the polishing tool 200 over the workpiece 10 may include straight, linear, arcuate zigzag, sinusoidal, rotary, spiral, or other programmable motions so as to enhance the removal rate of material from workpiece 10.

In performing polishing cycle 440 of process 400 of FIG. 7, there are several process parameters that will affect the removal rates and figure enhancement:

-   -   1. The rotational speed of the workpiece spindle 108 may be         controlled to give the effect of constant surface speed of         workpiece 10 similar to that of current CNC lathe technology, so         as to maintain a constant removal rate of material from the         workpiece 10. Such control of spindle speed eliminates the         effect of the decreasing or increasing diameter of the contact         circle made by the polishing tool 200 upon the rotating         workpiece 10, as it will be apparent that the surface speed at         the extremity (i.e. maximum diameter) of the rotating workpiece         is much greater than the surface speed near the center of the         workpiece. As the polishing tool 200 approaches the center of         the workpiece 10, the surface speed approaches zero; thus such a         variation in surface speed may be compensated for by varying the         rotational speed of workpiece spindle 108.     -   2. The speed/position of workpiece 10 may also be controlled so         as to improve rotational asymmetries of the workpiece during the         polishing cycle 440. For example, if there is an asymmetry that         requires more removal in a specific area of workpiece 10, then         the part spindle may slow or even stop in this area so as to         allow more removal by polishing tool 200. Alternatively, the         opposite situation may occur wherein less material removal is         required and the workpiece 10 may speed up during polishing in         this area to minimize the removal. In other terms, the dwell         time of the polishing tool 200 upon the workpiece 10 is adjusted         to selectively decrease or remove rotational asymmetries.     -   3. The “stiffness” of the polishing tool may be preset based         upon the inflation pressure within the bladder 204 of tool 200.         Depending on how “hard” or “soft” bladder 204 is made by         inflation pressure, the removal function of tool 200 will be         affected. Typically a stiffer polishing tool (i.e. higher         inflation pressure) will be used where higher removal functions         are required such as in processes where form error modification         of workpiece 10 is needed. Likewise, less inflation pressure         will be applied to bladder 204 in a final finishing process         where the best possible surface finish is required, at the         expense of a lower material removal rate. In a further         embodiment described previously, inflation pressure may be         varied in real time during the polishing cycle 440.     -   4. The compression factor may also be controlled in the         polishing cycle 440. Control of the compression factor is         achieved through the CNC program wherein the path the polishing         tool 200 is moved in a less compressed or more compressed path         (“tighter” or “looser path”) over the part, thereby affecting         its removal function and rate.     -   5. The tightness of the zigzag or circular motion of the         polishing tool 200 in its path over the workpiece 10 may also be         adjusted and varied throughout the polishing cycle 440. In one         embodiment, the compression factor is held constant while the         zigzag or circular motion of the polishing tool 200 is varied.         Circular and other motions such as e.g., zigzag, provide better         surface finish i.e. polish without leaving artifacts from the         tool/abrasive slurry in the surface ie, grooving.     -   6. The composition, rheological properties, PH, concentration,         and flow rate of polishing slurry delivered to the polishing         tool/workpiece during the process may be varied to affect         removal rates and surface roughness.     -   7. The size, shape, and material properties of the bladder 204         of polishing tool 200 significantly affects the process results         and capabilities depending on the workpiece 10 to be polished.     -   8. The material that the bladder is wrapped with (the foil 230)         is another variable, which will also affect the material removal         and finishing characteristics during polishing cycle 440.     -   9. The physical properties of the fluid medium used to         pressurize bladder 204 of tool 200 may be varied. Such physical         properties include specific gravity, shear viscosity, and         extensional viscosity. Variation of such properties between the         basic choice of a liquid or a gas is at least several orders or         magnitude. However, there is significant variation between         liquids, and there is opportunity for further control based on         the use of non-Newtonian liquids, such as shear or extensional         thickening liquids, shear or extensional thinning liquids,         visco-elastic liquids, and/or magneto-rheological liquids.

Using variations of the process parameters described in 1-9 above, the removal rates, the surface roughness, mid spatial frequency errors and figure error will be optimized during polishing cycle 440. Upon completion of polishing cycle 440, the machine 100 of FIG. 1 is stopped. Referring again to FIG. 7, and continuing again with process 400, the profile of the polished optic or other workpiece is measured in step 450, according to methods previously described. A decision is made at step 455, wherein if the optic 10 is acceptable against specifications, it proceeds through a step 490 of final measurement/quality control, and/or packaging, and shipping.

If such optic is not acceptable against specifications, steps are taken to prepare for another polishing cycle 440. Such steps include step 460, reprogramming of the CNC controller; optional step 470 of setting up/installing/and/or changing to a new polishing tool; and step 480, calculation of a new deterministic path for the next polishing cycle 440. The second polishing cycle then proceeds as previously described, and further iterations of steps 450-480 and 440 occur until the optic is polished to a condition that is acceptable against specifications, at which time step 490 is performed.

Included within the scope of the present invention is another embodiment of a polishing tool for the polishing of concave surfaces. FIG. 8A is a cross-sectional view of such a preferred polishing tool. Referring to FIG. 8A, polishing tool 300 comprises a mandrel 302 within which is disposed a groove 303 around the outer periphery of a flange 305 formed at one end of mandrel 302. Tool 300 further comprises a dome-shaped bladder 304, having a lip 307 that is disposed in groove 303 of mandrel 302. Compression washer 306 is fitter over the shank 301 of mandrel 302 and disposed against lip 305 of bladder 304. Locking nut 308 is threadedly engaged with a corresponding threaded portion of shank 301, such that locking nut 308 compresses lip 305 of bladder 304 into groove 303 of mandrel 302, thereby sealing bladder 304 to mandrel 302. Bladder 304 sealed to flange 305 of mandrel 302 thus forms a cavity 316 therebetween. Suitable materials for bladder 304 are e.g., natural or synthetic rubber, silicone, or polyurethane.

Numerous other embodiments of tool 300 are possible, wherein bladder 304 is formed such that bladder 304 fully encloses the outer surface 309 of the distal end of mandrel 302. In one embodiment, bladder 304 is conical, as indicated by dotted lines 311. In other embodiments, bladder 304 may have a parabolic shape, a hyperbolic shape, or combinations and transitions between hemispherical, conical (linear), hyperbolic, and parabolic surfaces at different radial zones along the surface of bladder 304. Thus bladder 304 may have a precisely hemispherical shape, a precisely conical shape, or a generally curved or domed shape formed by some combination of these various surface definitions. It will be apparent that even in the instance of a conically shaped bladder 304, that such bladder will likely be formed with a slight radius at the apex of such cone.

Mandrel 302 is further provided with an axial bore 312 disposed from the outer end 324 of shank 301 through the center of flange 305, such that the outer end 324 of mandrel 302 is in communication with cavity 316. Polishing tool 300 further comprises an inflation device 320 such as e.g., a check valve, or a tire valve stem, for providing a means to pressurize cavity 316 and maintain pressure therein, as previously described for tool 200 of FIG. 2A. Cavity 316 may be pressurized with any suitable fluid such as the liquids or gases previously described in this specification. In a further embodiment, axial bore 312 is connected during the polishing process to an adjustable pressure source, so that the pressure within cavity 316 may be varied in real time during the polishing operation, as described previously in this specification.

It will be apparent that in embodiments in which a relatively dense fluid, i.e. a liquid is used, and in which an elastic bladder is used, that the overall profile of the bladder, and therefore the spot size, can be varied as a function of polishing tool rotational speed. At relatively low rotational speed, a bladder with a substantially hemispherical shape will maintain such shape. As rotational speed is increased, the centrifugal force acting on the liquid contained in the bladder will deform the bladder into a flattened dome profile having a large radius of curvature near the center of the bladder, and a small radius of curvature near the lip 303 of the bladder. Such a feature can be used in the process of the present invention, wherein the polishing spot size is rendered adjustable as a function of rotational speed.

Referring again to FIG. 8A, polishing tool 300 further comprises a first ring or dome 332 of backing material disposed over the outer wall of bladder 304, and a second ring or dome 334 of polishing material adhered to dome 332, thereby forming a dual or composite ring or dome. In one embodiment, only a single ring or dome of material is used as the polishing medium, as described and shown for FIG. 4. Polishing tool is thus used in substantially the same manner as described for polishing tool 200 of FIG. 2A previously in this specification, with polishing tool 300 being the preferred tool for the polishing of concave surfaces. FIG. 8B is a side elevation view of the polishing tool of FIG. 8A, in the process of polishing a concave lens. Referring to FIG. 8B, it can be seen that the axis of rotation of polishing tool 300 is preferably disposed at an obtuse angle 50 with respect to the axis of rotation of concave lens 20, in order to achieve the desired contact between polishing surface 334 of toll 300 and concave surface 22 of lens 20.

FIG. 9 is a schematic representation of another preferred polishing apparatus for polishing concave spheres, aspheres, convex spheres, or other conformal shapes, such as lens 20 of FIG. 8B. Referring to FIG. 9, apparatus 150 is in one embodiment substantially similar to apparatus 100 of FIG. 1, with the main difference being provisions to contact the polishing tool with the concave surface of the workpiece. In order to accomplish this, the first preferred provision is the use of tool 300 of FIG. 8A, having a hemispherical, domed, or conical shape. A second preferred provision is in apparatus 150 wherein a B axis 152 directed into/out of the plane of FIG. 9 is provided, upon which polishing tool spindle 124 is mounted, and upon which polishing tool spindle 124 is bidirectionally rotatable, as indicated by arcuate arrow 154. Such a provision enables polishing tool 300 to be moved as indicated by arcuate arrow 156 into a position wherein the axis of rotation of polishing tool 300 is disposed at an obtuse angle 50 with respect to the axis of rotation of concave workpiece 20, as indicated in FIG. 8B. Such motion enables the polishing foil 334 of polishing tool 300 to contact the concave surface of a workpiece such as a concave lens or an asphere without having another portion of the polishing tool colliding with such workpiece.

It is to be understood that the machine 100 of FIG. 1, and the machine 150 of FIG. 9 that are provided to execute process 400 of FIG. 7, using tools 200 of FIG. 2A and tool 300 of FIG. 8A may have many different configurations. Axes types, spindle types, layout, size, provision of an automatic tool changer, and overall cost are just a few of the variables that could affect the desired design. While only show two specific possible machine configurations and specific possible tooling configurations are described in this specification and shown in FIGS. 1 and 9, it is to be further understood that many multi-axis CNC machine tools are known in the art, which can be suitably configured to use the polishing tools 200 and 300 and the process 400 of the present invention.

The overall computerized polishing process 400 using the apparatus 100 and polishing tool 200 of the present invention has many distinct advantages over prior art figure/polishing enhancement techniques, which are as follows:

-   -   1. There are numerous options available with respect to size and         shape of the bladder attached to the tool, such as a tire shape,         hemisphere shape, domed shape, conical shapes, cylindrical         shape, and the like. The shape of the bladder chosen depends on         the part geometry and the desired process results. There are         also options available in the choice of material composition and         properties of the bladder. These options of size, shape, and         material composition render the process of the present invention         very versatile.     -   2. Bladder inflation pressure is easily adjusted before the         process begins and for many polishing process requirements, no         pressure modification is required during the polishing process.         In the event that it is desirable to adjust bladder pressure         during the polishing process, a polishing tool and apparatus can         be made to provide such additional process versatility.     -   3. The method of inflating the bladder into the polishing foil         makes replacement of the foil very simple, and typically no         adhesive or mechanisms are required for attaching the foil to         the bladder. Adhesive is only required to attach the foil to the         PET ring.     -   4. In using the polishing tools of the present invention, many         types of materials may be wrapped around the bladder, thus         allowing for the use of a wide variety of polishing foil media.         Polishing foils may be made of e.g. polyurethanes, felts,         synthetics, corks, leathers, and many other materials, depending         on the desired polishing results. The foils may be impregnated         with cerium, diamond, alumina, pitch, etc.     -   5. The preferred method of placing the ring or foil upon the         bladder also allows for modification of the shape of the foil or         ring, i.e. the width, radius/contour or thickness thereof.     -   6. In the preferred embodiment, the poly(ethylene terephthalate)         ring that the foil may be attached to has not only great         strength but also long lasting flexibility, which greatly extend         the life of the polishing tool.     -   7. The concept of the bladder tool allows for flexibility so         that the polisher can conform to a variety of workpiece surface         geometries and still maintain contact/polishing action upon such         surfaces.     -   8. In contrast to small spot polishing tools, the bladder         polisher of the present invention will last and hold its shape         much longer in operation. A polishing ring of material, and not         just single spot develops the spot in the polishing tool and the         process of the present invention, so the polishing surface area         of the tool is greatly increased.     -   9. The compression amount and spot size of the polishing tool         can be easily adjusted by modifying the computer program to move         the tool closer or further from the part in its path over such         part.     -   10. Because of the variety of shapes and types of materials that         the various components of the polishing tool can be made from,         the polishing process of the present invention has the         flexibility to repair figure errors in a workpiece, and also         achieve the highest surface quality requirements of such         workpiece.     -   11. In instances where the process may require one or more         polishing tools to achieve the final results, this is easily         accomplished with known machine tool automatic tool changing         technology or multiple spindle technology, depending on the         configuration of the particular machine.     -   12. The powerful computer control algorithms provide the machine         operator with a variety of flexible programs which, depending on         desired results, can be easily modified and implemented, such as         e.g., zigzag, circular, orbital, elliptical tool paths.     -   13. Polishing of steels and other metallic components,         especially those used in injection molds, and thin film coating         dies can be done without the current technological limitations         of prior art polishing processes.

It is, therefore, apparent that there has been provided, in accordance with the present invention, a method and apparatus for correcting figure errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts. While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 

1. A polishing tool comprising a) a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; b) a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder; and c) a passageway disposed within said mandrel between said cavity and the exterior of said mandrel.
 2. The polishing tool as recited in claim 1, wherein said bladder comprises a first lip, said flange of said mandrel comprises a first groove, and said first lip is disposed and held within said first groove.
 3. The polishing tool as recited in claim 2, further comprising a washer engaged with said bladder, and a nut in contact with said washer and threadedly engaged with said mandrel.
 4. The polishing tool as recited in claim 2, wherein said passageway further comprises an axial bore having a first end in communication with the exterior of said mandrel.
 5. The polishing tool as recited in claim 4, wherein said cavity contains a liquid.
 6. The polishing tool as recited in claim 5, wherein said liquid is a viscous liquid.
 7. The polishing tool as recited in claim 4, wherein said passageway further comprises a radial bore in communication with said cavity and with said axial bore.
 8. The polishing tool as recited in claim 7, wherein said bladder comprises a second lip, said flange of said mandrel comprises a second groove, and said second lip is disposed and held within said second groove.
 9. The polishing tool as recited in claim 8, further comprising an inflation device disposed within said axial bore.
 10. The polishing tool as recited in claim 4 wherein said bladder is dome shaped.
 11. The polishing tool as recited in claim 4 wherein said bladder is cone shaped.
 12. The polishing tool as recited in claim 2, further comprising a polishing foil disposed on at least a portion of the exterior surface of said bladder.
 13. The polishing tool as recited in claim 12, wherein said polishing foil further comprises a first abrasive ring.
 14. The polishing tool as recited in claim 12, wherein said polishing foil further comprises a polishing ring assembly comprising a backer ring disposed on said portion of said exterior surface of said bladder, and an abrasive ring disposed on the exterior surface of said backer ring.
 15. The polishing tool as recited in claim 14, wherein said backer ring consists essentially of poly(ethylene terephthalate).
 16. The polishing tool as recited in claim 14, wherein said abrasive ring is impregnated with abrasive particles selected from the group consisting of ceria, alumina, silica, diamond, and mixtures thereof.
 17. An apparatus for polishing objects comprising: a) a first linear slide movable along a first axis, disposed upon a base; b) a first rotatable spindle engaged with said first linear slide, said first rotatable spindle further comprising a first chuck, and said first rotatable spindle aligned with said first axis; c) a second linear slide movable along a second axis, engaged with said first linear slide, with said second axis disposed orthogonally to said first axis; d) a second rotatable spindle engaged with said second linear slide, said second rotatable spindle further comprising a second chuck; and e) a polishing tool engaged with said second chuck of said second rotatable spindle, said polishing tool comprising a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder, and a passageway disposed within said mandrel between said cavity and the exterior of said mandrel.
 18. The apparatus as recited in claim 17, further comprising a third linear slide movable along a third axis, engaged with said first linear slide, and engaged with said second linear slide, with said third axis disposed orthogonally to said first axis and said second axis.
 19. The apparatus as recited in claim 18, wherein said second rotatable spindle is rotatable about an axis parallel to said third axis.
 20. The apparatus as recited in claim 17, further comprising a computer in control of said first linear slide, said second linear slide, said first rotatable spindle, and said second rotatable spindle.
 21. The apparatus as recited in claim 17 further comprising a fluid delivery system comprised of a reservoir, a pump, and a fluid conduit directed at said bladder of said polishing tool.
 22. The apparatus as recited in claim 17 further comprising a toolchanger.
 23. The apparatus as recited in claim 17, further comprising means to deliver a pressurized fluid to said passageway of said polishing tool.
 24. A method of polishing a surface of an object using a machine tool apparatus comprising a polishing tool comprised of a mandrel having a shank at a proximal end thereof, and at a flange at a distal end thereof; a bladder sealably engaged with said flange of said mandrel, defining a cavity contained between said flange and an inner surface of said bladder; and a passageway disposed within said mandrel between said cavity and the exterior of said mandrel, comprising the steps of: a) preparing said polishing tool for said polishing of objects; b) preparing and programming said machine tool for said polishing of objects; c) executing a first polishing cycle with said machine tool apparatus, wherein said polishing tool is in contact with said surface of said object; and d) measuring said surface of said object.
 25. The method as recited in claim 24, after said measuring of said surface of said object, further comprising the steps of reprogramming said machine tool, and executing a second polishing cycle with said machine tool apparatus.
 26. The method as recited in claim 24, wherein said step of preparing and programming said machine tool for said polishing of objects comprises the steps of: a) installing said polishing tool in said machine tool; b) entering polishing tool data into a controller of said machine tool; c) engaging said object having a surface to be polished with said machine tool; d) entering data on said object into said controller of said machine tool; e) analyzing a spot size function of said polishing tool on said object; f) programming said controller of said machine tool; and g) calculating the deterministic path of said polishing tool on said surface of said object.
 27. The method as recited in claim 26, wherein said deterministic path comprises a zigzag motion.
 28. The method as recited in claim 26, wherein said deterministic path comprises an orbital motion.
 29. The method as recited in claim 26, wherein said deterministic path comprises an elliptical motion. 